1. Field of the Invention
The present invention generally relates to a wireless sensor network, in particular, to a dual-mode wireless sensor network system, a key establishing method thereof, and an event processing method thereof.
2. Description of Related Art
In recent years, sensor networks have been broadly applied to the state monitoring of large-area objects, such as homeland security monitoring, environmental pollutant monitoring, and security monitoring at large construction sites (for example, the construction site of rapid transit system). In order to ensure the security of a monitored object, sensors continuously send detected states of the monitored object back to a system monitoring center (or an event processing device).
Conventionally, sensor networks can be categorized into wired sensor networks and wireless sensor networks according to the data transmission methods thereof. In a wired sensor network, sensor modules are connected to a monitoring center through physical connections (for example, network cables or optical fibers). The layout cost of a wired sensor network is very high, and it is very inconvenient to change the locations of sensors in the network. Thus, wireless sensor networks have been developed in recent years, wherein the sensor modules transmit data through wireless connections, and messages are relayed to the monitoring center through multiple wireless sensors.
Wireless sensors require no physical connection and accordingly are easy to be deployed, and a user can purchase wireless sensors and set up a home-based wireless sensor network easily. Thereby, it can be expected that in the near future, each family will have its own wireless sensor network. With the widespread of wireless sensor networks, wireless sensor networks of adjacent families are likely to overlap each other. How to appropriately separate the overlapped wireless sensor networks and effectively issue an abnormal event announcement when an abnormal event takes place while at the same time, protect the privacy of each family and prevent malice attack are the key points in the promotion of wireless sensor networks. Accordingly, a wireless sensor network system which offers both high privacy protection and effective abnormal event announcement is to be developed.